One of my players pointed this out to me recently that the spell Chaos Bolt does not require sight of a target, only that it is in range.  We rules in favor because it was cool for the moment and "chaotic", but as far as rules go, could you use this lack of wording to overcome invisibility or total cover?  You're still making a ranged spell attack, but it does not require them to see the target, therefore: 1. the lack of sight benefited by invisibility wouldn't apply, and 2. total coverage (such as hiding in a crate) would also not apply when sight doesn't matter to the spell's language.  

Thoughts?  

For reference: 
LEVEL: 1st
CASTING TIME: 1 Action
RANGE/AREA: 120 ft
COMPONENTS: V, S
DURATION: Instantaneous
SCHOOL: Evocation
ATTACK/SAVE: Ranged
DAMAGE/EFFECT: Acid (...)
You hurl an undulating, warbling mass of chaotic energy at one creature in range. Make a ranged spell attack against the target. On a hit, the target takes 2d8 + 1d6 damage. Choose one of the d8s. The number rolled on that die determines the attack’s damage type, as shown below.

d8 Damage Type
     1 Acid
     2 Cold
     3 Fire
     4 Force
     5 Lightning
     6 Poison
     7 Psychic
     8 Thunder
If you roll the same number on both d8s, the chaotic energy leaps from the target to a different creature of your choice within 30 feet of it. Make a new attack roll against the new target, and make a new damage roll, which could cause the chaotic energy to leap again.

A creature can be targeted only once by each casting of this spell.

At Higher Levels. When you cast this spell using a spell slot of 2nd level or higher, each target takes 1d6 extra damage of the type rolled for each slot level above 1st.

This is true regarding being able to target an invisible creature if you have some other means of knowing where that creature is, such as you've been audibly tracking the noise that it makes while it moves.

However, total cover still wins.  There is a general spellcasting rule that requires a "clear path" to the target when the spell is cast and this rule still applies even if you do not necessarily have to see the creature.

If a spell doesn't specifically state that it requires the target to be seen, like Chaos Bolt, then they can be cast at creatures that are Invisible or otherwise unseen.

However, such an unseen creature still benefits from being unseen: https://www.dndbeyond.com/sources/basic-rules/combat#UnseenAttackersandTargets

So if the character doesn't know the location of the target they must declare a location at which they are directing their attack. If the target isn't there the attack automatically misses. If they guessed correctly or know where the creature is then they have disadvantage on the attack roll.

A creature hiding behind a wall still benefits from Total Cover and it is a general rule for all spells that there must be a clear path between the caster and the target: https://www.dndbeyond.com/sources/basic-rules/spellcasting#AClearPathtotheTarget

If a caster attempts to target something on the other side of a wall or similar obstacle, then the spell impacts the obstruction. This can have unanticipated affects if the spell was something like Fireball.

In general, spells that require spell attack rolls don't require you to be able to see the target.

Quote from 6thLyranGuard >>

In general, spells that require spell attack rolls don't require you to be able to see the target.

Yep.

You can swing a sword (melee weapon attack) or throw a dagger or loose a crossbow (ranged weapon attacks) at an unseen foe, you just have to guess the locations and roll the attack at disadvantage. The same applies to melee spell attacks and ranged spell attacks. Firing a scoching ray or chaos bolt at an unseen target is possible, as is using a flame blade or a spriitual weapon. Guestimate a location, roll the attack (probably at disadvantage).

Quote from 6thLyranGuard >>

In general, spells that require spell attack rolls don't require you to be able to see the target.

Yeah, it's the same wording on eldritch blast, fire bolt etc.

Line of sight and line of effect for magic are two different things - and this is something 5e never really covers well.  It's also a campaign setting specific answer that depends on your background.

Attacking an invisible target RAW is quite possible IF you can pin down that target to a specific square or at least area (fireball has it's uses....)

Attacking a target creature that has total cover is generally not possible RAW but you also don't have line of sight in that case.

Scenarios where a target is "in range" but don't have line of effect usually involve some sort of barrier between the spellcaster and the target 

This tends to be a campaign specific answer based on how you want magic to work in your setting.  Magic doesn't NECESSARILY have to have a "straight path to the target", but if it isn't a straight line path and requires an attack roll you are definitely justified in giving the shooter disadvantage on the roll.

If the spell in question can target an area as well as a creature your caster may be able to fire the spell around the corner blind by targeting an area.. There's got to be a tactical reason to take fire bolt vs eldritch blast beyond just energy type after all...

Quote from Greenstone_Walker >>

You can swing a sword (melee weapon attack) or throw a dagger or loose a crossbow (ranged weapon attacks) at an unseen foe, you just have to guess the locations and roll the attack at disadvantage. The same applies to melee spell attacks and ranged spell attacks. Firing a scoching ray or chaos bolt at an unseen target is possible, as is using a flame blade or a spriitual weapon. Guestimate a location, roll the attack (probably at disadvantage).

Actually, you don't have to guess the location by default when attacking an unseen target.  You would only have to do this if the target is Hidden or is for some other reason both unseen and unheard and therefore has an unknown location.  Disadvantage does apply though.

Thank you for your feedback, everyone.  I appreciate the insight.  

It worked out well in our setting since the BBEG was under total cover inside a construct and the player's fury aimed to hit them and made them hurt.  To hit roll beat both the AC of the BBEG and construct.  My player was rolling very well, so I doubt disadvantage would have changed things.  

While Chaos Bolt doesn't target a creature you can see, disadvantage to attack roll from being unseen or invisible as well as cover can still apply, wether it's AC bonus or being imprevious to spell's effect and attacks.

The general assumption for an attack roll is you must be able to see the creature.  You 'can' guess, but there has to be some sort of logical reason for you to attack that 'location', and seeing the miniature on the board that is 'invisible', that would be metagaming and not in the spirit or intent of the game.  

That said, yes you can target creatures you don't see.  Just like an arrow, but you have to get really lucky or have intel (The ranger who can see invisible creatures shouts "It's over there, right next to the blue barrel.  Blast it!")

Quote from Wyldeshot >>

The general assumption for an attack roll is you must be able to see the creature.

 

 And you know what happens when someone assumes?

There's no requirement that someone be able to see a creature they're attacking.  Invisible/unseen creatures are not undetected unless they're actively hiding, and if a creature isn't hidden then you know its location, no rolls necessary.  You just take disadvantage on any attack rolls made against it.